The present invention relates to a circuit arrangement for a hydraulic brake system including anti-lock control (ABS) and traction slip control by brake management (BASR), an electromotively driven hydraulic pump for the auxiliary pressure supply in the ABS mode and BASR mode, sensors to determine the wheel rotational behavior, and an electronic circuit for analyzing the sensor signals and generating braking pressure control signals and auxiliary pressure control signals.
Prior-art hydraulic brake systems of this type have a hydraulic pump which supplies both the auxiliary pressure required during anti-lock control (in the "ABS model") and the braking pressure for the brake actuation during traction slip control (in the "BASR model"). The hydraulic pump can have a one-circuit or multiple-circuit design and is driven by an electric motor. This motor is switched on when the control commences. The hydraulic energy requirements vary widely depending on the control operation and the control phase. Of course, the nominal capacity of the motor-and-pump assembly is dictated by the maximum requirements which may occur in certain, rare situations. Compared to an anti-lock control operation, principally, a substantially lower amount of hydraulic pressure and a correspondingly lower amount of energy is required for traction slip control by brake management (BASR) when the pump must supply the pressure for the actuation of the brake. Although a less potent motor-and-pump assembly would be sufficient for traction slip control, for cost reasons, the same assembly is used for ABS and BASR operations.
Noises which develop upon the commencement of the control and are caused by the activation and the operation of the hydraulic pump are felt as a disturbance, in particular, during a traction slip control operation. Frequently, other noises are superimposed during the anti-lock operation, so that the pump noises are less significant. Also, it is known to minimize disturbing noises by reducing the rotational speed of the pump or the motor of the pump, which is proportional to the flow rate of the pump (DE 40 32 876 A1). Therefore, attempts have been made to reduce the flow rate of the pump in the BASR operation, when principally a reduced flow rate compared to the ABS operation is required, by inserting a series resistance into the activation path of the engine pump (DE 41 10 494 A1). However, in this event, too, the flow rate of the pump is dictated by the maximum output required in the BASR operation. In most situations, the flow rate and, thus, the development of noises continue to be considerably greater than necessary. Hence, a better adjustment to the actual flow rate requirements is desirable.